Rotaviruses have been studied extensively in many parts of the world predominantly by crosssectional approaches. Such studies have yielded essentially "numerator" data which indicated that rotaviruses are a major cause of diarrheal illness in infants and young children. There has been a paucity of longitudinal viral gastroenteritis studies that yield not only important "denominator" data but also valuable insights into the natural history of pathogen or illness, with special emphasis on epidemiologic, immunologic and laboratory data. We, therefore, initiated an intensive examination of anal swab and serum specimens obtained during a previous LID long-term longitudinal study (1955-1969) at Junior Village, a welfare institution for homeless, but otherwise normal children. Anal swabs and blood specimens were obtained routinely from the youngest age groups, which ranged from 6 months to about 5 years of age during various periods of the study. Surveillance was carried out by a trained medical staff. Children were housed in cottages according to their age. The scope of the surveillance of about-45-100 infants and young children can be appreciated by the fact that in the 1966 period of the study, a full-time medical staff of 2 nurses and 4 practical nurses from out unit were in daily attendance, in addition to the full-time medical staff of the District of Columbia Department of Public Welfare that included nurses, practical nurses, and a full-time physician in charge of medical care at Junior Village. Rectal temperatures were obtained on each child daily; routinely, a physician examined any child with a rectal temperature of 100.6 degrees F or greater. Careful medical records were kept by the nursing staff on all children. Thus, with this background we plan to investigate the natural history of rotavirus infections in a longitudinal manner.